exp save: Support --message.

Custom commit message to use when committing the experiment.

Part of #8870

dvc/commands/experiments/save.py

@@ -16,6 +16,7 @@ class CmdExperimentsSave(CmdBase):
                 name=self.args.name,
                 force=self.args.force,
                 include_untracked=self.args.include_untracked,
+                message=self.args.message,
             )
         except DvcException:
             logger.exception("failed to save experiment")
@@ -75,4 +76,11 @@ def add_parser(experiments_subparsers, parent_parser):
         help="List of untracked paths to include in the experiment.",
         metavar="<path>",
     )
+    save_parser.add_argument(
+        "-M",
+        "--message",
+        type=str,
+        default=None,
+        help="Custom commit message to use when committing the experiment.",
+    )
     save_parser.set_defaults(func=CmdExperimentsSave)

dvc/repo/experiments/executor/base.py

@@ -277,6 +277,7 @@ class BaseExecutor(ABC):
         info: "ExecutorInfo",
         force: bool = False,
         include_untracked: Optional[List[str]] = None,
+        message: Optional[str] = None,
     ) -> ExecutorResult:
         from dvc.dvcfile import LOCK_FILE
         from dvc.repo import Repo
@@ -308,6 +309,7 @@ class BaseExecutor(ABC):
                 exp_hash,
                 exp_name=info.name,
                 force=force,
+                message=message,
             )
             ref: Optional[str] = dvc.scm.get_ref(EXEC_BRANCH, follow=False)
             exp_ref = ExpRefInfo.from_ref(ref) if ref else None

dvc/repo/experiments/save.py

@@ -16,6 +16,7 @@ def save(
     name: Optional[str] = None,
     force: bool = False,
     include_untracked: Optional[List[str]] = None,
+    message: Optional[str] = None,
 ) -> Optional[str]:
     """Save the current workspace status as an experiment.
 
@@ -29,7 +30,10 @@ def save(
 
     try:
         save_result = executor.save(
-            executor.info, force=force, include_untracked=include_untracked
+            executor.info,
+            force=force,
+            include_untracked=include_untracked,
+            message=message,
         )
         result = queue.collect_executor(repo.experiments, executor, save_result)
     finally:

tests/func/experiments/test_save.py

@@ -153,3 +153,10 @@ def test_untracked_dvclock_is_included_in_exp(tmp_dir, scm, dvc):
     exp = dvc.experiments.save()
     fs = scm.get_fs(exp)
     assert fs.exists("dvc.lock")
+
+
+def test_exp_save_custom_message(tmp_dir, dvc, scm):
+    setup_stage(tmp_dir, dvc, scm)
+
+    exp = dvc.experiments.save(message="custom commit message")
+    assert scm.gitpython.repo.commit(exp).message == "custom commit message"

tests/unit/command/test_experiments.py

@@ -628,7 +628,7 @@ def test_experiments_save(dvc, scm, mocker):
     assert cmd.run() == 0
 
     m.assert_called_once_with(
-        cmd.repo, name="exp-name", force=True, include_untracked=[]
+        cmd.repo, name="exp-name", force=True, include_untracked=[], message=None
     )